April 2006 | NTIA Technical Memo TM-06-439
Frank Sanders; J. Randy Hoffman; Yeh Lo
Abstract: In response to interference from an S–band (2700–2900 MHz) airport surveillance radar (ASR) to a meteorological (weather) radar in the same band, measurements were performed at the field location of the two radars to determine the interference mechanism and any possible mitigation options. Measurements included emission spectra of the ASR and observations of the interference energy in the RF front–end and IF stages of the weather radar. Measurement results showed that interference energy originated in the unwanted emissions of the ASR (i.e., front–end overload was not occurring in the weather radar). But the problem was exacerbated by the placement of a passive diode limiter ahead of a bandpass filter in the weather radar receiver's RF front–end. The interference could not be mitigated unless the front–end configuration of the weather radar was modified. With the necessary modification completed, the interference was successfully mitigated by installing a conventional notch filter on the ASR's output stage, the notch being tuned to the weather radar frequency. It is recommended that the front-end configuration of all weather radars of the type in question should be immediately changed in the same way as the weather radar in this study, and that appropriate output filters should be installed in ASRs that are located in close proximity to these weather radars to mitigate interference effects at all sites in the U.S.
Keywords: Radar Spectrum Engineering Criteria (RSEC); airport surveillance radar interference; radar co-channel interference; radar emission spectrum measurements; radar interference mechanisms; radar interference mitigation; RF front-end overload; weather radar interference
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Frank H. Sanders
Institute for Telecommunication Sciences
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